A Prospective Study of the Nonmedical Use of Prescription Medications by Adolescents is in response to current PA-08-127 (previously PA-07-123). It builds on the research team's previous cross-sectional, exploratory research (RO3 DA018272: RO3 DA 018239) focusing on gender differences in the nonmedical use of scheduled, prescription medications (NUPM) among adolescent and young adult populations. In previous exploratory studies,our research team observed notable heterogeneity among nonmedical users, captured by subtypes characterized by: a) either possession of a legal prescription (or not a legal prescription) and b) motivations (self-treating versus sensation-seeking). While all four subtypes are characterized by volition, two NUPM subtypes involve motives to self-treat, while two other NUPM subtypes involve motives related to sensation-seeking. Additionally, NUPM may involve one's own prescription medication or alternatively, someone else's. The study aims are guided by a theoretical model, drawn from Problem Behavior Theory, which depicts the domains of risk that may lead to NUPM and its consequences. A mixed-method design is proposed; the study includes annual, cross-sectional, web-based surveys over five-years and a longitudinal, panel study that includes face-to-face, semi-structured interviews. The study aims to: 1) investigate the prevalence of medical adherence and the four subtypes of NUPM, the co-occurrence among the subtypes of NUPM, and demographic characteristics associated with each type; 2) identify common patterns of NUPM behaviors across each drug classification (sleep, stimulant, anxiety/sedative, pain); 3) examine the stability/instability of group membership across the 5 points of assessment and the extent to which early trajectories of drug use are associated with substance abuse problems and 4) determine the extent to which the qualitative data converge with quantitative data. Data from this study should be invaluable in planning for new prevention efforts aimed at reducing NUPM among adolescents.